1. Field of the Invention
The present invention relates to an actutor for a microatomizer and, in particular, to an actuator component for a piezoelectrically operated microatomizer, to methods of producing such an actuator component as well as to a microatomizer which makes use of such an actuator component.
2. Description of Prior Art
Elements for atomizing liquid media, which will simply be abbreviated to atomizers in the following, are used in many technical fields, e.g. in the cosmetic industry for atomizing hair sprays and perfumes, in the field of medicine as medicament sprays, in connection with various coating techniques for atomizing varnishes and adhesives, in the field of chemistry for atomizing liquid reagents, and in the field of domestic engineering as room air humidifiers.
Most of the atomizers used at present work by means of mechanical atomization in the case of which the liquid is pressed through a valve of suitable shape and size due to a mechanically generated overpressure. This has the effect that the medium, i.e. the liquid to be atomized, is discharged in the form of small droplets, in most cases statistically distributed, and forms a mist of liquid. The necessary overpressure is produced manually by a pumping process, e.g. in perfume atomizers, or by the use of excess pressure reservoirs, e.g. propellants in hair sprays.
In addition to the above-described mechanical systems, also electrically driven nebulizers exist; these electrically driven nebulizers are based on piezoelectric substrates which are electrically caused to vibrate. In the course of this process, a liquid on the surface of the piezoelectric substrate is atomized by the capillary waves produced.
In xe2x80x9cMicromechanical Ultrasonic Liquid Nebulizerxe2x80x9d written by R. Paneva et al, Sensors and Actuators A 62 (1997), pp. 765 to 767, a piezoelectric atomizer is described in which a thin silicon diaphragm is caused to vibrate by means of a piezoelectric ZnO layer; in the course of this process, liquids are atomized by the thin silicon diaphragm. The atomizer described in this publication operates at a vibrational frequency of 80 to 86.5 kHz, the atomizer disclosed there producing droplets of very different diameters.
All the existing mechanical and piezoelectric systems have one main drawback insofar as the droplet diameters vary over a wide range. Especially in medical applications, this is a severe drawback. Droplets can only be taken up by the lungs when they have a diameter of approx. 1 to 5 xcexcm. All the known systems achieve this only to a certain extent so that the commercially available atomizers have an efficiency of only 10% up to 15% at the most, i.e., when known atomizers are used, a volume which is ten times as large must be atomized so that the amount of medicament required for the patient will be transferred to the patient""s lungs. In addition, the volume atomized in individual dosing processes varies over a large range in known atomizers.
All the known mechanical atomizers have the additional drawback that nozzles have to be used which clog very easily. This is the reason for the fact that mechanical systems are always throw-away products. Moreover, the use of nozzles increases the likelihood of maloperation, a circumstance which, especially from the medical point of view, is disadvantageous or even dangerous in acute situations.
In xe2x80x9cFlxc3xcissigkeitszerstxc3xa4ubung durch Ultraschallxe2x80x9d, in Elektronik October 1979, pp. 83 to 86, the ultrasonic atomizing effect is described, which functions according to the principle of capillary wave theory.
DE 19802368 C1 describes a microdosing device in which a pressure chamber is delimited by a diaphragm on one side thereof, the pressure chamber having provided therein an inlet opening and an outlet opening. Suitable driving of the diaphragm has the effect that, for a dosing process, fluid is sucked in through the inlet opening and ejected through the outlet opening. This microdosing device operates on the basis of a displacement effect, but not on the basis of the capillary wave theory.
DE 69404004 T2 discloses a piezoelectric nebulizer in which the liquid is applied to an atomization grid, which is caused to vibrate; for applying the liquid, a soft component having a capillary or feltlike structure, such as an open-cell foam, is used.
In WO-A-95/15822 an atomizing device is described, which is based on an atomization making use of the capillary wave theory. A diaphragm is here caused to vibrate so as to effect the atomization. A liquid to be atomized is supplied through openings in the diaphragm, which fully penetrate the whole diaphragm, to the diaphragm surface from which the liquid is atomized.
It is the object of the present invention to provide a microatomizer permitting, on the one hand, mass production, and, on the other hand, the atomization of defined-diameter droplets with increased efficiency, as well as a method for producing such a microatomizer.
According to a first aspect of the invention this object is achieved by a piezoelectrically-driven, capillary wave-theory microactuator comprising:
a diaphragm formed in a semiconductor substrate;
a piezoelectric actor arranged on a surface of the diaphragm so as to cause said diaphragm to vibrate; and
a passage formed in said semiconductor substrate and used for supplying a liquid to be atomized from an inlet end to the diaphragm surface located opposite to said piezoelectric acuator, wherein, due to the vibrations of the diaphragm, the liquid supplied to the surface of the diaphragm is atomized on the basis of the capillary-wave theory and ejected through an outlet arranged in opposed relationship with said diaphragm, said passage being formed by at least one groove-like structure which does not fully penetrate the substrate and which is provided in the surface of the substrate from which the liquid supplied is atomized.
The actuator component used in the atomizer according to the present invention makes use of the piezoelectric principle. For this purpose, a piezoelectric layer produced preferably in thin-film technology is used for deflecting a thin diaphragm which is preferably etched in silicon, the thin diaphragm being caused to vibrate in this way. The silicon substrate, in which the diaphragm is formed, has additionally formed therein a passage means which serves to supply the liquid to be atomized so as to cause a substantially uniform wetting of the diaphragm surface located opposite the piezoelectric actuator. Due to the fact that liquid is supplied through the passage means according to the present invention in such a way that the diaphragm is wetted in a substantially uniform manner, the droplet diameters are prevented from varying over a wide range in accordance with the present invention. The actuator component of the atomizer according to the present invention is preferably adapted to be driven at a frequency between 2 and 2.5 MHz and in such a way that the droplets produced by the atomization have a diameter between 1 and 5 xcexcm. In order to achieve this, the geometrical dimensions of the diaphragm, the supply of liquid as well as the vibration frequency used are suitably adapted as atomization parameters for adjusting a desired droplet size.
Depending on the size of the diaphragm, it may be of advantage in accordance with the present invention to implement the passage means such that it will supply the liquid to be atomized to the diaphragm from different directions. The diaphragm may, for example, be rectangular, the passage means supplying the liquid to be atomized then via the four corners of the diaphragm.
A microatomizer according to the present invention making use of such an actuator may comprise a holder to which the actor component is fixed in such a way that the inlet end is in fluid communication with a fluid supply conduit, that the passage means is sealed by the holder with the exception of a fluid communication existing between the passage means and a fluid supply conduit and the passage means and the diaphragm surface located opposite the piezoelectric-actuator, and that an opening of the holder is provided in the area of the diaphragm surface located opposite the piezoelectric-actuator, the opening being used for ejecting the atomized liquid.
The holder is implemented such that the actuator can easily be attached thereto, the fluid supply conduit leaving the holder preferably in a direction opposite to the ejection direction of the atomized liquid.
According to a further aspect of the present invention, the above object is achieved by method of producing a piezoelectrically-driven, capillary wave-theory microatomizer used for atomizing on the basis of the capillary-wave theory a liquid supplied to a surface of a diaphragm, said method comprising the following steps:
a) producing an actuator by the following sub-steps:
a1) applying a piezoelectric actuator to a main surface of a semiconductor substrate;
a2) patterning the semiconductor-substrate main surface located opposite the piezoelectric actuator so as to define therein the diaphragm which has arranged thereon the piezoelectric actuator, and at least one passage in the form of a groove like structure which does not fully penetrate the substrate and which extends from an inlet end to said diaphragm; and
b) fixing the actuator to a holder such that the diaphragm surface located opposite the piezoelectric actuator faces an opening in said holder.
It follows that the present invention provides an actuator for a piezoelectrically driven microatomizer, which, due to the use of use of micromechanical means and especially due to the use of silicon technology, permits a very small and economy-priced system that can be produced in very large numbers of pieces. The above-described properties of the atomizer have the effect that the distribution of the droplets, the precision of the volume to be atomized and thus, in the case of medical applications, the medical efficiency are improved substantially. The actuator does not need a nozzle so that clogging effects are excluded. The system is therefore also suitable to be used more than once; in this case, it will suffice to exchange a fluid reservoir which is connected to the fluid supply line. In view of the fact that the piezodrive needs little energy, energy consumption is reduced as well.
Further developments of the present invention are specified in the dependent claims.